Composition for temporarily protecting metal components from corrosion, its processes of preparation and of application, and metal components obtained from this composition

ABSTRACT

The invention concerns a composition useful for providing temporary protection against corrosion to metal surfaces comprising an oil-in-water emulsion characterised in that said emulsion contains in its aqueous phase at least a compound of general formula (I) in which the groups R, R 1  and R 2  represent independently of one another a hydrogen atom, a C 1 -C 20  alkyl group, a C 1 -C 20  halogenoalkyl group with the halogen being chlorine, bromine, iodine or fluorine, a C 3 -C 6  cycloalkyl group, a carboxylic function or a C 1 -C 6  carboxyalkyl group; n is a whole number varying from 1 to 3; and X represents an oxygen or sulphur atom in the form of one of its soluble salts. The invention also concerns a method for preparing said composition, its method of application to the surface of metal part and the resulting part.

A subject-matter of the present invention is a composition of use intemporarily protecting metal components from corrosion, a process forthe preparation of the said composition and the metal components coatedwith a dry film deriving from this composition.

The problem of the temporary protection of metal surfaces and moreparticularly of sheet metal from atmospheric corrosion is a constantpreoccupation of manufacturers. Multiple possibilities therefore alreadyexist for conferring, on the surface of the metal sheet, a form oftemporary protection by fatty films, in particular based on conventionalprotecting oils.

However, the increase in the requirement criteria of users has led steelmanufacturers to provide increasingly elaborate solutions which takeinto account highly varied factors (appearance, suitability for surfacetreatment, cleanliness of the premises, safety, toxicology and thelike). These imperatives have thus been partially satisfied by thedevelopment of a non-fatty coating and of its method of application, thequalities of which confer properties of temporary protection fromcorrosion of the order of two months on the metal sheet thus treated (FR92 08 037).

However, there remains a demand on the part of users for coatings whichexhibit an even better corrosion stability, without, of course,prejudicing the subsequent properties of use, and in particular possessa prolonged corrosion stability with, preferably, a corrosion resistanceof greater than three months.

It is a specific object of the present invention to provide a novelcoating in accordance with these requirements.

A first approach consists in incorporating one or more corrosioninhibitors in coatings has base of formulations of oils for temporaryprotection.

Conventionally, the corrosion inhibitors present in protecting oils arechosen from:

amino compounds of alcoholamine type,

sulphonate derivatives, such as their barium or sodium salts, oralkylbenzenesulphonates, and

acids of linoleic type.

Unfortunately, the increase in corrosion resistance obtained with theseconventional inhibitors is not satisfactory.

There consequently remains to this day a need for a method for thetemporary protection of metal components which is significantly improvedin terms of corrosion resistance (greater than three months), a dryappearance and suitability for surface treatment, with or withoutpreparation, and which, in addition, conforms to the toxicology rules(absence of barium, of heavy metal salts, and the like).

Thus it is that the Applicant Company has demonstrated that theincorporation within an oil-in-water emulsion of a heterocyclicthioether of saturated carboxylic acids, as corrosion inhibitor, wouldmake it possible specifically and satisfactorily to meet all theserequirements.

More specifically, the present invention relates to a composition of usein conferring temporary protection from corrosion on metal surfacescomprising an oil-in-water emulsion, characterized in that the saidemulsion comprises, in its aqueous phase, at least one compound ofgeneral formula I

in which formula the R, R₁ and R₂ groups are, independently of oneanother, a hydrogen atom, a C₁ to C₂₀ alkyl group, a C₁ to C₂₀ haloalkylgroup, with the halogen being able to be fluorine, chlorine, bromine oriodine, a C₃ to C₆ cycloalkyl group, a carboxyl functional group or a C₂to C₆ carboxyalkyl group,

n is an integer varying from 1 to 3, and

X is a sulphur or oxygen atom,

in the form of one of its water-soluble salts.

It is preferably a compound of general formula I in which R is ahydrogen atom and X a sulphur atom.

Unexpectedly, the addition of a corrosion inhibitor in accordance withthe present invention to an oil-in-water emulsion confers a corrosionresistance on the corresponding coating which is very significantlyprolonged over time. This improvement is in fact much greater than thatexpected, that is to say that equivalent to the superimposition of therespective effects of the emulsion and of the said inhibitor in terms ofcorrosion resistance. It is advantageously the reflection of a synergybetween the two components.

The novelty of the claimed composition is additionally based on theincorporation of a compound of general formula I in the aqueous phaseand not in the lipid phase of the emulsion employed in the claimedcomposition. This compound, which is water-insoluble in nature, istherefore present in the composition in a neutralized form for thepurpose of conferring a satisfactory solubility in water on it.

This neutralization of the compound or compounds of formula I employedaccording to the invention can be carried out conventionally by a personskilled in the art. It can be obtained, for example, from aqueousammonia, morpholine, ethanolamine, ethanol or potassium hydroxide.Depending on the reagent employed, it may be necessary, if appropriate,to adjust the pH of the final composition to a value compatible with therecommended application, that is to say to a value of between 8.2 and9.5 and preferably between 8.5 and 9. This can be easily carried out byadjusting the pH of the final emulsion by a further addition ofneutralizing agent, such as ethanolamine, for example.

The corrosion inhibitor of general formula I is preferably present inthe claimed composition in a proportion of 1 to 10 g/l and preferably of1 to 3.5 g/l.

Mention will very particularly be made, as preferred compounds ofgeneral formula I, of the water-soluble salts ofbenzothiazolylthiosuccinic, α-(benzo-thiazolylthio)stearic,α-(benzooxazolylthio)lauric, α-(benzothiazolylthio)caproic andα-(benzothiazolylthio)-caprylic acids.

It is more preferably a water-soluble form of benzothiazolylthiosuccinicacid (BTSA) and more specifically its ammonium or ethanolamine salt.

As regards the emulsion, it can be defined as comprising, in dispersionin water, 3 to 13% by volume of an oily phase comprising from 75 to 90%by volume of at least one oil and from 5 to 10% by volume of at leastone surface-active agent. If appropriate, a supplementary corrosioninhibitor can be present in a proportion of 5 to 15% by volume in theoily phase.

The emulsion preferably comprises, in dispersion in the aqueous phase,between approximately 3 and 8% and preferably approximately 6% by volumeof an oil.

The oil present in the oily phase of the emulsion can be composed of amineral, vegetable or animal oil.

It is advantageously a mineral oil and preferably an oil of paraffinicor naphthenic type or a mixture of these.

Mention will very particularly be made, as mineral oil preferablyemployed according to the present invention, of the soluble oil Aquasafe21® from Castrol.

It is preferable to use, as surface-active agent of the oily phase, asurfactant of polyoxyethylene type.

Use is advantageously made, as corrosion inhibitor of the oily phase, ofa carboxylic acid, a barium or sodium alkylsulphonate or a fatty acidamine salt.

According to a preferred form of the invention, the claimed compositioncomprises, as corrosion inhibitor, a water-soluble salt ofbenzothiazolylthiosuccinic acid (BTSA) present, at a concentration ofbetween 1 and 3.5 g/l and preferably of the order of 2.5 g/l, in theaqueous phase of an emulsion comprising 6% of soluble oil which ispreferably the oil Aquasafe 21® from Castrol. It is preferably theammonium salt of benzothiazolylthiosuccinic acid present at aconcentration of the order of 2.5 g/l.

The present invention also relates to a process for the preparation ofthe said composition.

More particularly, this process is characterized in that the compound orcompounds of general formula I are incorporated in the form of anaqueous solution in the aqueous phase of the emulsion prior to itsemulsification with the oily phase.

This is because the Applicant Company has noticed, unexpectedly, thatthe method of incorporation of the compound of general formula I in theemulsion has a significant effect on the anticorrosion activity of thecorresponding composition. Thus it is that it proves to be particularlyadvantageous to introduce this compound of general formula I into theemulsion in the form of an aqueous solution. It thus remains dispersedin the aqueous phase of the emulsion. This is because it has beenobserved that the addition of this compound directly to the oily phaseof the said emulsion significantly affected the anticorrosion behaviourof the resulting composition. This effect is more specificallydemonstrated in Examples 7 and 9 below.

Another subject-matter of the present invention is a process fortemporarily protecting metal components from corrosion.

More particularly, this process is characterized in that it comprisesthe stages consisting in:

applying a composition according to the invention to at least a part ofthe said metal component, and

drying the said coated metal component until a dry film is obtained.

According to a favoured form of the invention, the composition accordingto the invention is applied to the surface of the metal component so asto saturate its absorption sites with compounds of general formula I andthat, on conclusion of the heating of the said composition, in order toobtain a film therefrom, compound of general formula I is not foundpresent in the thickness of the applied film.

This is because the performance of the coating film proves to bemarkedly improved if the application of the claimed composition to themetal plate to be treated is carried out so as to saturate itsadsorption sites with a compound of general formula I and to prevent theaccumulation of this same compound of general formula I in the thicknessof the film.

It is therefore desirable to adapt its method of application so as tooptimize this saturation of the adsorption sites of the treated surfaceand to minimize, on the other hand, the concentration of compounds ofgeneral formula I in the thickness of the emulsion film after drying.The parameters to be considered, for this adjustment of theconcentration of the claimed composition at the surface of the treatedplate, are the desired thickness of the film and the concentration ofoily phase and of compound of general formula I in this composition. Itis within the scope of a person skilled in the art to carry out thisadjustment by routine operations taking into account these variousparameters.

The adjustment of the optimum concentration of inhibitor of generalformula I at the surface of the metal component to be treated can, forexample, be assessed and carried out in the following way, after havingapplied and dried, at the surface of the component, a compositionaccording to the invention with a predetermined concentration ofcorrosion inhibitor(s) of general formula I. The component is leachedwith acetone, by steeping or by spraying. The level of saturation of theadsorption sites at the surface of the treated metal component is thenmeasured by running an infrared spectrum of the leached component usingthe technique of 80° grazing incidence Fourier transform infrared (FTIR)spectroscopy. The fact that an interfacial film rich in inhibitors ofgeneral formula I remains or does not remain on conclusion of thisleaching, as well as the residual thickness of this film, are alreadyindices with regard to the degree of adsorption of the said inhibitor.By comparison with infrared spectra run on other components treated withcompositions exhibiting different concentrations of inhibitor andleached in the same way, it is subsequently possible to determinewhether or not the adsorption sites of the metal surface are saturated,that is to say whether the concentration of inhibitor is sufficient inthe composition to produce an effective treatment.

It is subsequently confirmed that a composition has not been applied tothe component which is so concentrated in inhibitor that saturation ofthe adsorption sites would have been exceeded to the point where asignificant portion of the inhibitor of the composition would be foundin the thickness of the dry film applied to the metal surface. To thisend, the content of inhibitor in the leachate is analysed, for examplealso by infrared spectroscopy. By comparison with infrared spectra runon leachates originating from other components treated with compositionsexhibiting different concentrations of inhibitor and leached in the sameway, it is then possible to determine whether the concentration ofinhibitor in the composition is too high to produce an effectivetreatment.

The concentration of inhibitor in the composition is thus adjusted.

The aqueous composition according to the invention can, of course, bedeposited in the form of a film at the surface of the metal componentsto be protected by any appropriate conventional means of roller coatingdevice type or similar or alternatively by spraying. The component thustreated is subsequently dried in order to obtain a dry film inaccordance with the invention.

This heating can be carried out, for example, by bringing the treatedcomponent to a temperature of between 50 and 100° C. for a time varyingbetween approximately 20 seconds to 10 minutes.

Another subject-matter of the present invention is a metal componentcoated with a dry film for temporary protection from corrosion obtainedfrom the claimed composition and/or in accordance with the claimedprocesses.

The surface density of dry film at the surface of the componentpreferably varies between 0.3 and 2 g/m² and more preferably is of theorder of 0.5 g/m².

Within the meaning of the invention, the term “metal components” isunderstood to mean moderately thick hot rolled plates, hot rolled thinmetal sheets, cold rolled steel sheets and various types of steel platesand sheets, in particular of bare steel.

As stated above, the metal components coated with a dry protective filmwith a composition as defined according to the invention prove to beresistant to corrosion and display good suitability for stamping andbonding. What is more, the dry films obtained according to the claimedprocess display good properties of adhesion with regard to substrates ofvaried natures, at the surface of which substrates they are capable ofbeing applied at their surface.

Furthermore, the coatings deriving from the claimed compositions havetribological performances which are satisfactory and thereforeadvantageous with regard to stamping. Thus it is that theircharacterization in terms of friction shows that they exhibit a reducedcoefficient of friction in comparison with conventional coatings.

The compositions according to the invention can, in addition, be appliedeffectively to metal plates which are already coated with a dry film andtherefore prove to be particularly advantageous in treating externalturns and edges of a coil which are already coated with a non-fattycoating or in protecting pickled metal components.

Other advantages of the claimed composition will become apparent onreading the examples presented below without implied limitation of thepresent invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: Characterization of the optimum concentration of inhibitor ofgeneral formula I,

FIG. 2: Impedance characterization of films according to the inventionand of control films,

FIG. 3: Friction characterization of a film according to the inventionand of control films,

FIG. 4: Characterization of the adsorption power of a corrosioninhibitor of general formula I at the surface of a metal component,

FIGS. 5 and 6: Characterization of the adsorption power of variousinhibitors, including BTSA.

I—MATERIAL AND METHOD A) Material

A. 1—Corrosion inhibitors tested

1) Benzothiazolylthiosuccinic acid in accordance with the invention,sold by Ciba under the name Irgacor 252.

The dissolution of the inhibitor BTSA in an oily emulsion is carried outafter neutralization with aqueous ammonia or with ethanolamine.

By way of example, in order to neutralize and therefore dissolve 1 g ofinhibitor in one litre of water, a minimum of

2 ml of aqueous ammonia or

0.2 ml of ethanolamine is needed.

These amounts of neutralizing agent can subsequently be increased (by afew tenths of an ml) in order to obtain a final pH (of the emulsion) ofbetween 8.2 and 9.5.

2) Irgacor L184 and Irgamet 42 from Ciba.

Irgacor L184

This is a polycarboxylic acid amine salt of general formula as follows

It is generally used with Irgamet 42, which is also soluble in water andof general formula as follows

The proportion is 1 volume of Irgamet 42 per 19 volumes of Irgacor L184(cf. compositions 4 and 5 in Table I below).

3) RC 305®, sold by Croda.

This is an aqueous mixture of alcoholamines of amine borates comprising70% water.

4) PX 2881®, sold by Elf.

It is composed of an aqueous mixture of sodium heptanoate and ofheptonoic acid with perborate.

5) SER AD FA 379, sold by Servo group Hüls.

This is a mixture of several inhibitors provided as paint additive. Itscomposition is as follows:

10-25% of C₁₂-C₁₄ (2-benzothiazolylthio)succinic acid tert amine salts

10-25% of ethoxylated tridecylalcohol phosphate-comprisingmonoethanolamine salts

10-25% of zinc salts of branched (C₆-C₁₉) fatty acids

<2.5% of zinc salts of naphthenic acid

10-25% morpholine benzoate.

These inhibitors 1 to 5 are employed as additives in an emulsioncomposed of a soluble mineral oil and of water.

A. 2—Emulsion

The mineral oil employed is the soluble oil Castrol Aquasafe®.

It is composed of 80 to 95% of a mineral base (naphthenic andparaffinic). Surfactants are incorporated in this product in order torender it emulsifiable in water (anionic surfactant, sodiumalkylsulphonates).

This soluble oil is diluted to 6% in demineralized water and the pH ofthe emulsion thus obtained is 9.2.

A. 3—Formulations Tested

Their compositions appear in Table I below.

TABLE I Typical Typical concentration 1 concentration 2 Composition(soluble oil) (inhibitor(s)) -1- Castrol 6% 0 Aquasafe 21 (60 g/l)emulsion (soluble oil alone) -2- (BTSA) 0 Aqueous solution (inhibitoralone) 30 g/l -3- Composition 1 + 6% 2.5 g/l composition 2 (60 g/l) -4-Irgacor L184 + 0 30 g/l (L 184) and Irqamet 42 1.5 g/l (I 42) -5-Composition 1 + 6% 30 g/l (L 184) and composition 4 (60 g/l) 1.5 g/l (I42) -6- Composition 1 + 6% 15 ml/l PX2881 (60 g/l) -7- Composition 1 +6% 5 ml/l PX2881 (60 g/l) -8- Composition 1 + 6% 15 ml/l RC305 (60 g/l)-9- Composition 1 + 6% 5 ml/l RC305 (60 g/l)

B) Methods

B 1—Electrochemical Measurement of Impedance—Transfer Resistance

The performances of the various compositions tested are assessed byapplying them to test specimens of pickled steel, polished with G600paper, in proportions such that the final grammage deposited on testspecimens is of the order of 500 mg/m² (0.5 μm). The test specimen issubsequently immersed in an electrolyte composed of demineralized waterand of 1% by weight of sodium chloride (NaCl). The steel test specimenis held in the electrolyte for 30 min in order to stabilize itselectrochemical potential. After 30 min, using a potentiostat, afrequency analyser, a reference electrode and a counterelectrode, asinusoidal perturbation in potential (in mV) is imposed on the testspecimen for various decreasing frequencies and “the response intensity”(in μA/cm²) is measured.

It is thus possible to obtain impedances (Z =U/l for the variousfrequencies and to draw impedance diagrams. From these diagrams, atransfer resistance (ohm.cm²) can be deduced therefrom and can becompared to a “corrosion resistance”.

Experimental parameters - Reference electrode saturated calomelelectrode - Counterelectrode platinum electrode - Working electrode 7cm² steel test specimen - Potentiostat EGG 273 ® potentiostat -Frequency analyser Schlumberger 1255 ® - Sinusoidal perturbation ±5 mVin amplitude - Test potential corrosion potential - Frequencies from100,000 Hz to 0.2 Hz

B 2—Validation by “Humidotherme FKW” Test (DIN 50017 Standard)

To do this, steel test specimens, coated with the various compositionsto be tested, are suspended in a chamber with the following cycle

1 cycle=8 hours at 40° C. and 100% humidity

16 hours at 20° C. and 75% humidity

The number of cycles before the appearance of corrosion is thusrecorded. The thickness of the films applied is 0.5 g/m² on average (0.5μm). Without contrary indications, the composition is always composed ofCastrol Aquasafe 21 soluble oil diluted to 6% in demineralized water.

B 3—EB1 Area and Finishing Area Test

The test specimens are exposed to the atmosphere of 2 storage areas

finishing area area with a relatively mild atmosphere (closed doors)

EB1 area very harsh area because the test specimens are exposed close tothe openings to this area and are therefore subjected to a high humiditywhen it rains, to exhaust gases from lorries and to steelworks dust.

In both cases, the number of days before the appearance of corrosion isrecorded.

EXAMPLE 1

Determination of the Optimum Concentration of Inhibitor with Regard toCorrosion Stability

Inhibitor BTSA, neutralized with ethanolamine, is introduced atconcentrations varying between 0.5 and 20 g/l in the aqueous phase intoa composition according to the invention comprising an aqueous emulsionbased on 6% Castrol Aquasafe 21 oil. The corrosion resistances of thevarious corresponding compositions are determined by Humidotherme FKWaccording to the procedure described in Material and Method. The resultsobtained are represented in the graph in FIG. 1.

Optimum resistance is observed with the composition comprising 2.5 g/lof inhibitor BTSA in the neutralized form.

EXAMPLE 2

Appraisal of the Corrosion Resistance After Atmospheric Exposure

This appraisal is carried out with a composition according to theinvention comprising a concentration of BTSA of 2.5 g/l (composition 3)and in comparison with the control compositions 1, 2 and 4, identifiedmore specifically in the chapter Materials and Methods.

These compositions are subjected to EB1 area and finishing area tests,the protocols for which are explained in Materials and Methods.

The results observed with each of the compositions are presented inTable II below.

TABLE II Number of days Number of days before the before the appearanceof appearance of corrosion (EB1 corrosion Composition area) (finishingarea) 1 15 to 25 days 66 days 2 2 to 6 days 15 days 3 30 to 65 days 110days  4 3 days 5 10 to 20 days

It is noticed that only the composition according to the invention, thatis to say composition 3, comprising a salt of BTSA in an aqueousemulsion, exhibits a resistance which is significantly prolonged overtime. What is more, the increase in the resistance observed is markedlygreater than that resulting from the superimposition of the resistancesinduced respectively by the emulsion and by BTSA considered inisolation. There is advantageously a synergy in their respectiveeffects.

EXAMPLE 3

Appraisal of the Resistance According to a Transportation Test

This test is also carried out on the compositions 1, 2, 3 and 4,identified more specifically in the chapter Materials and Methods.

This test consists in stacking test specimens which have been coatedbeforehand with the solutions to be tested. The stacks are held clampedin order to simulate the contiguous turns of a steel coil or the stackedsheets of a pile of metal sheets.

The pile of stacked test specimens (“clamped pile”) is subsequentlyintroduced into a programmed climatic chamber in order to carry out analternation of 32 h cycles (“transportation cycle”).

Breakdown of the transportation cycle (1 cycle =32 hours)

10 h at 40° C. and 95% RH

4 h at 20° C. and 80% RH

10 h at −5° C. and 0% RH

8 h at 30° C. and 85% RH

In the “transportation cycle” configuration, the tests are carried outon clamped piles under the following conditions:

each scenario is represented by 4 test specimens,

observations are made every three cycles. The piles are opened and thecondition of the interfaces is observed.

The results appear in Table III below.

TABLE III Number of cycles before the Compositions appearance ofcorrosion 1 <6 cycles 2 <6 cycles 3 >19 cycles  4 <6 cycles 5 <6 cycles

Only the metal component coated with a composition according to theinvention, that is to say composition 3, displays a significantlyimproved corrosion resistance. Furthermore, this increase reflects asynergy between the emulsion and the BTSA salt.

EXAMPLE 4

Validation for Humidotherme Test

Validation is carried out according to the protocol described in thechapter Materials and Methods on the compositions 1 to 9 defined in thissame chapter.

Apart from the compositions 2 and 4, based on an aqueous solutionrespectively comprising BTSA and an Irgacor L184/Irgamet 42 mixture, thetested compositions are always composed of Castrol Aquasafe 21 solubleoil diluted to 6% in demineralized water (composition 1) with variousinhibitors added (compositions 3 and 5 to 9).

The results presented in Table IV below are observed.

TABLE IV Number af cycles before the Compositions appearance ofcorrosion 1 12 cycles 2  1 cycles 3 >22 cycles   4  1 cycle 5 <12cycles   6 12 cycles 7  8 cycles 8 12 cycles 9 15 cycles

By this test, it is confirmed that the various control inhibitors testeddo not have the effectiveness of the product BTSA. The existence of asynergy solely between an inhibitor of general formula I and of anAquasafe 21 emlsion is also confirmed by this test.

EXAMPLE 5

Appraisal of the Corrosion Resistance Through the Transfer Resistance

This test was carried out by drawing up the electrochemical impedancediagrams of the compositions 1 and 3 identified in the chapter Materialsand Methods, tested according to the protocol described in this samechapter. The results appear in Table V below.

TABLE V Transfer resistances in Compositions kΩ.cm² 1 10 to 20 kΩ.cm² 360 to 120 kΩ.cm²

EXAMPLE 6

Effect of the Concentration of BTSA Salt in the Interfacial Film on theCorrosion Resistance

Impedance curves were drawn up, according to the protocol described inthe chapter Materials and Methods, for metal components coated with thefollowing compositions:

2) emulsion alone

3) emulsion +5% aqueous BTSA solution, without drying

4) emulsion +5% aqueous BTSA solution, then drying at 60° C. in order toobtain a 650 mg/m² film

5) emulsion +3.5% aqueous BTSA solution, then drying at 60° C. in orderto obtain a 250 mg/m² film

6) emulsion +3.5% aqueous BTSA solution, then drying at 60° C. in orderto obtain a 700 mg/m² film.

In the emulsions 3 to 6, the BTSA is present in a form neutralized withaqueous ammonia. Drying of the emulsions 4 to 6 therefore results inevaporation of ammonia.

The results are presented in FIG. 2, with the real part of the impedanceexpressed on the abscissa and the imaginary part of the impedance on theordinate.

From examination of these curves, it emerges that, at equivalent filmthickness, a better behaviour is observed with a film obtained with 3.5%of BTSA (composition 4) than 5% of BTSA (composition 6). An excess ofBTSA in the resulting film therefore has an unfavourable effect.

Furthermore, it may be noted that carrying out a drying stage(composition 4) confers an advantageous behaviour on the correspondingfilm in comparison with a film which has not been subjected to drying(composition 3). This effect is in fact related to the use of BTSAneutralized with aqueous ammonia.

EXAMPLE 7

Effect of the Preparation Protocol on the Effectiveness of a CompositionAccording to the Invention

The performances of a composition prepared according to the process ofthe invention and of a composition prepared by addition of BTSA to thesoluble oil prior to its emulsion are compared in terms of corrosionresistance. The results are presented in Table VI below.

TABLE VI Transfer Transpor- resistances EB1 area Humidothermes tationR_(T) test FKW test test kΩ.cm² Composition. 30 to >22 cycles >19 cycles70 2.5 g/l of BTSA 65 d diluted in the 6% emulsion 2.5 g/l of BTSA 45 d20 cycles 15 cycles 20 diluted in the maximum soluble oil beforeemulsion. Emulsion subsequently prepared

The total resistances are determined by electrochemical impedance,carried out according to the protocol described in the preceding chapterMaterial and Method.

From these results, it emerges that the method of addition of the BTSAto the composition according to the invention has a not insignificanteffect.

In equal amounts, if it is dissolved in the soluble oil beforeemulsifying, the performance is significantly reduced in terms ofcorrosion resistance.

EXAMPLE 8

Friction Characterization of the Compositions Provided

The single-pass friction tests are carried out with plane-planefriction, at a variable transversable pressure of 200 to 2000 daN, withtools made of high-speed steel with an area of 1 cm². The rate ofdisplacement is 2 mm/s.

The test specimens are cut from pickled hot metal sheets, grade BS2,with a thickness of 2 mm.

The performances of two compositions according to the invention arecompared with two control compositions, the tribological behaviour ofwhich compositions appears in FIG. 3.

Composition A: a protecting oil used on steel sheets as protection fromcorrosion (Quaker 8021), deposited in a proportion of 2 g/m²

Composition B: the Aquasafe 21 soluble oil at 6% in water, deposited ina proportion of 500 g/m²

Composition C: Composition B with organic inhibitor BTSA added in thesalt form (pH of the solution between 7.2 and 8.5), deposited in aproportion of 500 mg/m²

Composition D: identical to Composition C, the pH of which is stabilizedbetween 8.5 and 9 by the addition of ethanolamine, deposited in aproportion of 500 mg/m².

The friction curves improve with Compositions C and D. The resultsobtained are better than with a protecting oil having stampingproperties (Composition A).

EXAMPLE 9

Characterization of the Adsorption Power of the Inhibitor BTSA

According to a first method, wettability measurements are carried out ontwo compositions, a composition based on an Aquasafe 21 emulsion(Control) and a composition based on an Aquasafe 21 emulsion to whichhas been added BTSA (BTSA) at a concentration of 2.5 g/l in the form ofits neutralized salt, the pH being of the order of 8.5 to 9.

The test consists in depositing a drop of each of the emulsions on asteel test specimen and in monitoring the change in contact angle of thedrop (monitoring of the spreading).

The graph represented in FIG. 4 shows that a drop of Aquasafe 21emulsion to which BTSA has been added (BTSA) spreads much more quicklyover the steel than a drop of conventional Aquasafe 21 emulsion(Control). These results show that BTSA acts as a spreading agent. Itcontributes to rendering a film more homogeneous and to giving it agreater covering power.

This adsorption power is also assessed by infrared spectrum according tothe following protocol and with the compositions defined below in TableVII.

In all cases, the tested compositions comprise an emulsion exhibiting aconcentration of Aquasafe 21 oily base of 5%.

TABLE VII Concentration BTSA pH of the Composition of BTSA dissolved in:emulsions A 0.25% oil 9.7 B 0.125% oil 10.1 C 0.25% emulsion 9 D 0.75%emulsion 8.9 E 3.75% emulsion 10.2

The emulsions A, B, C, D and E are applied to polished test specimens.In order to study the film-steel interface, the infrared spectrum is runon the test specimen after leaching with acetone (grazing incidence FTIRspectra, 80° angle of incidence). It is thus observed that

the films A and B are completely removed by the leaching. It maytherefore be deduced therefrom that the inhibitor is weakly adsorbed inthe case of these compositions.

after leaching the films C, D and E, an interfacial film remains, thethickness of which increases with the initial concentration ofinhibitor. Likewise, the content of inhibitor in these residualinterfacial films (base oil+inhibitor) increases with the finalconcentration.

This test therefore confirms that it is preferable to add the inhibitorBTSA to the Solclean emulsion and not to the base oil beforeemulsification (Composition C in comparison with A). Thus, the inhibitorcan be strongly adsorbed on the steel and have an optimum effect. Thesespectra are perfectly consistent with the corrosion tests.

From their examination, it also emerges that the performances are poorerwhen BTSA is found in the thickness of the film of dried oil, that is tosay in the effluents from the leaching. This is particularly the casewith the composition E, which comprises 3.75% of BTSA.

EXAMPLE 10

Comparison of the Adsorption Power or of BTSA With Respect to OtherWater-soluble or Water-solubilized Corrosion Inhibitors

The effect of the concentration of BTSA neutralized with ethanolamine inaqueous solution, applied to a bare steel sheet, is compared with thatof the inhibitors RC 305, PX 2881 and SER AD FA 379 identified in thechapter Material and Method. This effect is assessed by electrochemicalmeasurements of impedances according to the protocol described above.The various inhibitors are tested at between 0.5 and 20 g/l and thetransfer resistances (“corrosion resistance”) obtained are representedin the graphs in FIGS. 5 and 6. It appears that only the inhibitor BTSAexhibits an optimum adsorption peak at the surface of the bare metalsheet, with the peak centred on 2.5 g/l. As regards the other inhibitorstested, they display an increasing effectiveness with concentration butan effectiveness which is always inferior to that of BTSA (30,000 Ω·cm²at 2.5 g/l). As regards the inhibitor SER AD FA 379, the content of BTSAin this inhibitor is too low to observe results in accordance with theinvention in the inhibitor concentration range under consideration.

This behaviour of the inhibitors in aqueous solution can in fact beextrapolated to corresponding solutions, comprising an oily phase,according to the invention.

What is claimed is:
 1. Composition for conferring temporary protectionfrom corrosion on metal surfaces comprising an oil-in-water emulsioncomprising, in its aqueous phase, at least one compound of generalformula I

in which formula the R, R₁ and R₂ groups are, independently of oneanother, a hydrogen atom, a C₁ to C₂₀ alkyl group, a C₁ to C₂₀ haloalkylgroup, with the halogen being chlorine, bromine, iodine or fluorine, aC₃ to C₆ cycloalkyl group, a carboxyl functional group or a C₁ to C₆carboxyalkyl group, n is an integer varying from 1 to 3, and X is asulphur or oxygen atom, in the form of one of its water-soluble salts,characterized in that the said emulsion is obtained by emulsification ofan aqueous phase, in which the said compound of general formula I hasbeen incorporated beforehand, with an oily phase.
 2. Compositionaccording to claim 1, wherein the compound of general formula I isselected from the water-soluble salts of benzothiazolylthiosuccinic,α-(benzothiazolylthio)stearic, α-(benzathiazolylthio)lauric,α-(benzothiazolylthio)caproic and α-(benzothiazolylthio)caprylic acids.3. Composition according to claim 1, wherein the compound of generalformula I is a water-soluble salt of benzothiazolylthiosuccinic acid. 4.Composition according to claim 3, wherein said water-soluble salt is anethanolamine or ammonium salt.
 5. Composition according to claim 1,wherein the pH of said composition is between 8.2 and 9.5. 6.Composition according to claim 1, wherein the emulsion comprises, indispersion in water, 3 to 13% by volume of an oily phase comprising from75 to 90% by volume of at least one oil, and from 5 to 10% by volume ofat least one surface-active agent.
 7. Composition according to claim 1,wherein the emulsion comprises, in dispersion in the aqueous phase,between 3 and 8% by volume of an oil.
 8. Composition according to claim6, wherein the oil present in the oily phase of said composition is amineral oil.
 9. Composition according to claim 1, wherein the compoundof general formula I is present in the said composition at aconcentration of between 1 and 10 g/l of emulsion.
 10. Compositionaccording to claim 1, which comprises between 1 to 3.5 g/l of saidcompound of said general formula I.
 11. Composition according to claim1, which comprises between 1 and 3.5 g/l of benzothiazolylthiosuccinicacid in the form of a water-soluble salt in the aqueous phase of anemulsion comprising 6% of soluble oil.
 12. Composition according toclaim 11, wherein said water-soluble salt is an ammoniumbenzothiazolythiosuccinate, present at a concentration of the order of2.5 g/l.
 13. Process for temporarily protecting a metal component fromcorrosion, which comprises the stages consisting in: applying acomposition according to claim 1 to at least a part of the said metalcomponent, and drying the coated metal component so-obtained until a dryfilm is obtained.
 14. Process according to claim 13, wherein thecomposition is applied so as to saturate the adsorption sites at thesurface of the metal component with a compound of general formula I andin that, on conclusion of the drying of the said composition, in orderto obtain a dry film therefrom, the compound of general formula I is notfound present in the thickness of the applied film.
 15. Metal componentcoated with the dry film for temporary protection from corrosionobtained according to the process of claim
 13. 16. Metal componentaccording to claim 15 with a surface density of dry film of between 0.3and 2 g/m².
 17. Metal component coated with the dry film for temporaryprotection from corrosion obtained from a composition as definedaccording to claim
 1. 18. Composition according to claim 6, whichfurther comprises in the oily phase from 5 to 15% by volume of acorrosion inhibitor.
 19. Composition according to claim 18, wherein thecorrosion inhibitor of the oily phase is a carboxylic acid, a barium orsodium alkylsulphonate or a fatty acid amine salt.
 20. Compositionaccording to claim 8, wherein the oil is at least one selected from thegroup consisting of parrafinic and naphthenic oil.